The bloodsucking fish may not be the vertebrate ancestor we thought

Derped from the side and hellish from below, the lamprey is the bane of the Great Lakes fishing industry. A jawless, blood-sucking fish, the lamprey is often considered an ancestral primitive vertebrate for its rudimentary morphology and larval stage. Now a team of researchers have written a new study of fossilized lamprey larvae from the Devonian period which they say shows lamprey evolution happened differently than previously thought. This would mean that we would need to change our origin history of vertebrates.

The researchers’ paper was published Wednesday in the journal Nature. Their argument depends on the life cycle of the lamprey. Modern lamprey larvae, called ammocoetes, are blind filter feeders, which later turn into their predatory, gnarled adults. Biologists and paleontologists saw that the larval stage of ammocoetes was a relic of the early evolution of vertebrates, and a sign that the lamprey could be considered a living fossil that helps explain where all the backed animals came from. bony. But the recent team describes fossils of lampreys that are not ammocoetes – these fossils look like smaller versions of adult lampreys – suggest that this larval stage was a later evolutionary adaptation, unique to lampreys.

“Now it looks like lampreys are the weirdest,” Tetsuto Miyashita, a paleontologist at the Canadian Museum of Nature and lead author of the article, said during a video call. “[The lamprey] seems primitive, more primitive than those extinct jawless fish. But it was the other way around.

Miyashita’s team describes four different species of ancient lampreys from Africa and North America, between 360 and 310 million years old. At the time, the localities of Montana, Illinois and South Africa (where eel-like lampreys were excavated) were shallow seas; a different habitat from the freshwater in which most lampreys squirm today.

The non-ammocoite fossil lamprey was not a smaller group of adult lamprey, according to the team, as some of the fossilized fish even have yolk sacs still attached to their bodies. If it was just at one site, “we would have thought we were looking at this really weird, specialized, extinct lamprey line that did its own thing and possibly lost the filtering larval phase,” Miyashita said. “But species after species after species, across four different lineages of fossil lamprey, they show the same thing.”

The authors suggest that the larval stage of the ammocete is an adaptation that the lamprey has developed to move in freshwater environments in which it grows too well. During the twentieth century, many efforts were made to control the invasive lamprey population in the Great Lakes. First observed in Lake Ontario in 1835, lampreys spread to the other large lakes in the mid-20th century. Now the established population is wreaking havoc on trout, whitefish, cisco and other lake fish species, clinging to them with their suckers, ultimately killing them. In the 1960s, annual fish catches in the Great Lakes were 2% of their previous average; a dramatic nose attributed to lampreys.

“These species, like the lamprey, which we think of as ‘ancient fish’ have been evolving for as long as we have and are not frozen in time,” Jera said.miah Smith, a University of Kentucky biologist who was not affiliated with the recent article, in an email. “More broadly, the study clearly shows the importance of considering alternatives to widely accepted evolutionary scenarios, and how new data sets continue to shape our understanding of the deep evolutionary history of the vertebrate lineage.”

For an alternative candidate for a vertebrate ancestor, researchers suggest the armored Devonian fish called ostracoderms, which look a lot like warring tadpoles.

“Lampreys aren’t quite the swimming time capsules we once thought they were,” co-author Michael Coates, a biologist at the University of Chicago, told a Canadian museum of nature. Press release. “They remain important and essential for understanding the deep history of vertebrate diversity, but we must also recognize that they too have evolved and specialized in their own right.”

This story has been updated to include comments from Jeramiah Smith.